The aim of this research is to examine the analgesic properties of some morphine-related compounds. The extent to which these drugs effect sensitivity to a painful stimulus will be analyzed separately from the extent to which they effect the behavioral response to pain. The effects of chlorpromazine, diazepam and amphetamine will also be examined for comparative purposes because of their marked effects on responding in many behavioral situations. Two procedures will be used: (1) a shock intensity titration procedure and (2) a shock intensity discrimination procedure. In the titration procedure the level at which animals will maintain a continuously increasing shock stimulus will be examined. In the signal detection procedure, discrimination performance will be examined with several different shock intensity levels and under conditions in which the consequences of different responses are varied. This research will attempt to develop animal models for examining analgesics which will (1) elucidate the basic and important variables operative in the perception of and the behavioral response to pain and (2) be useful in screening drugs with potential analgesic properties which may alter either the perception of pain or the organism's response to it.